Black Hole PDS 70 is a T Tauri star about 370 light-years away and only 5.4–5.5 million years old — still a cosmic infant, slightly cooler than the Sun. Two giant planets have already been photographed in its disk, making the system a rare live snapshot of planet formation. JWST later found water vapor in the innermost part of that disk, right where rocky worlds could form. The puzzle was how the water got there. A new look at archival HARPS spectra revealed the clue: variable lines of neutral sodium. They appear and vanish over a few nights, only partly cover the star, and belong to gas moving faster than PDS 70 itself. That is a poor match for a steady disk wind, but a good match for icy bodies on stretched orbits heating up as they swing close to the star and shedding gas by sublimation — in other words, exocomets. Models suggest the system’s gas giants can fling those icy bodies inward from the cold outer disk, delivering water to the terrestrial zone. Something similar may have happened in the early Solar System. If the interpretation holds, PDS 70 is the youngest known example of this process around a star not far from the Sun in temperature: a still-forming planetary system already being watered by comets.
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